The complete operating range of the compressor includes stable and unstable conditions, and the boundary between the two is the stall and surge line. Previously, the two were modeled in isolation from each other. The unsteady flow equation of the compression system is constructed based on the idea of the body-force model. It is possible to obtain the steady characteristics and transient simulation of post-stall, realizing the unified simulation of the full working conditions of the compression system. Among them, by using and developing the elementary cascade method, the continuity of correlation method for the body-force source term in different flow regions is realized. The model was validated on four single-stage compressors as well as one two-stage compressor, and the results showed that the steady-state characteristics, stable boundary, and rotating stall characteristics obtained by the developed model were in good agreement with the experimental results. The experiments showed that when the blade solidity was increased, the compressor's work capacity increased and its stability improved, and the rotational frequency of the stall cell increased slightly. The calculated results always agreed with the trend of the experimental results. In addition, the variation of blade forces during rotating stall can be easily obtained using the concept of body force and more details of the flow field can be obtained using the model.

The onset of rotating stall and surge in compressors limits the operating range of aero-engines. Accurately predicting the key features during these events is critical in the engine design process. In this paper, a three-dimensional computational model for transient simulation of multi-stage axial compressors during stall is proposed. The kinetic equations describing the dynamic process of the compression system are constructed, with a 3D through-flow model for the compression part and a 1D gas collector model for the outlet part. The calculation of the source term is performed using the developed body-force model, which realizes the correlation between the deviation angle and the loss coefficient with the inlet parameters in various flow regions. Validated on a single-stage compressor and a single-rotor fan, the results show that the method is capable of capturing the stall and surge features correctly and that the three-dimensional structure of the stall cell can be captured. In addition, this model could be used for the analysis of the surge load, which is significant for the structural integrity of the compressor.

The inlet swirl distortion and non-uniform tip clearance have great effects on aero-engine performance and stall margin. In this paper, the effects of paired swirl distortion on the aerodynamic stability and stall inception of a single stage axial compressor with non-uniform tip clearance are quantitatively analyzed by using the swirl distortion descriptors. The experimental results show that the paired swirl distortion dominated by co-rotating swirl improves the stability of the axial compressor. For a single-stage axial compressor with eccentricity of 100%, the stall inception starts at the maximum tip clearance with clean inlet. The initial position of the stall inception is determined by the maximum tip clearance when the small intensity paired swirl distortion exists at the compressor inlet. As the swirl intensity increases, it shifts towards the position of the counter rotating swirl vortex core. The inlet swirl will not change the type of stall inception.

In this paper, an experimental study was carried out on the rotating instability in an axial compressor subjected to inlet steady paired swirl distortion. In order to deepen the understanding of the rotating stall mechanism under inlet steady paired swirl distortion, the dynamic-wall static pressure near the rotor tip was monitored to characterize the flow in the rotor tip region at different circumferential stations. In the experiment, the dynamic characteristics of the rotor tip flow field at a stable operating point and during the process from the stable point to complete stall were measured. The results indicated that for the compressor with a 2 mm rotor tip clearance, the inlet paired swirl distortion induced rotating instability (RI) near the stall point, causing the compressor to enter stall in advance. Compared with the RI intensity of the clean inlet, the distortion with a swirling blade stagger angle (αst) of ±20° increased the RI intensity up to 69.8%, while for αst equal to ±40°, the RI intensity increased at most by 135.8%. As the rotor tip clearance increased to 3 mm, the co-rotating swirl in the paired swirl distortion inhibited the appearance of RI, while the counter-rotating part aggravated the development of RI. At the beginning, the process of the compressor rotating stall involved the alternation of short-scale disturbance and long-scale disturbance. The co-rotating swirl weakened the perturbation propagated from the counter-rotating swirl sector. Once the inhibition was no longer present, the short-scale disturbance rapidly developed into a long-scale disturbance and then entered the rotating stall.

For the five degree-of-freedom (5-DOF) AC active magnetic bearing (AMB), which is a multivariable, nonlinear and strongly coupled system, conventional single-variable controller cannot meet the control requirements. Based on the state space model of 5-DOF AC AMB and direct feedback linearization, the equations of coordinate transform and nonlinear state feedback can be simplified into differentiating output equations, which achieves the input-output linearization of 5-DOF AC AMB system. Then, the system can be decoupled into five independent 2-order linear subsystems and realizes the completely decoupling of 5-DOF. Finally, the internal model control (IMC) method is employed to synthesize the subsystems, in order to avoid the performance deteriorated due to the model error and external disturbance. The results of simulation example demonstrate that this decoupling control strategy can realize not only the dynamic decoupling of 5-DOF AC AMB, but also the good dynamic/static performance and robustness.